In order to correct false indications in the case of pulsating flows, for example in the intake tract of an internal combustion engine, the following methods are used.
A correction map is stored in the engine control unit of the internal combustion engine, which can be addressed via the characteristic quantities of the speed of the internal combustion engine (measured via a speed sensor) and the load (e.g. the throttle valve opening position). In addition, nonlinear optimized characteristic curves are used in engine control units.
Raw signals UHFM of an air mass detector are detected in that the air mass detector is exposed to an air mass flow m at different operating points on an engine test bench and the signal generated by the air mass detector is recorded. The raw signals UHFM of the air mass detector are converted into air mass flow values by interpolation on an output characteristic. Subsequently, average values of the air mass flow values are formed via integral multiples of a pulsation period for the respective operating points of the internal combustion engine, given by the speed and the specific output. A deviation dm/m, which corresponds to the average deviation of the average air mass flow of a comparison air mass flow, is calculated for the respective operating points (n, pME) of the internal combustion engine. Subsequently, the quadratic norm (X2) over the matrix of the deviation is calculated. An adjusted characteristic curve in the sense of an optimization is produced, the characteristic curve being optimized with respect to the condition that the quadratic norm (X2) becomes a minimum. The raw signals UHFM of the air mass detector are converted into air mass flow values by interpolation to the adjusted characteristic curve, several of the above-mentioned method steps being iteratively run through by repetition.
A flow meter is known from German Published Patent Application No. 197 43 340. The flow meter takes the form of a measuring tube through which the medium to be measured flows, the medium being exposed to at least one ultrasonic transmitter/receiver unit. At least one reflector is situated in the measuring tube for reflecting an ultrasonic signal sent by an ultrasonic transmitter/receiver unit either directly or via a reflection on a measuring tube wall in the direction of the same or of other ultrasonic transmitter/receiver units. To avoid surface waves in the reflection, an angle of incidence of the ultrasonic signal on a reflector, measured between a normal to the surface and a reflector and the incident ultrasonic signal, is provided, which is greater than a Rayleigh angle or the material properties of the reflectors have an appropriately high Rayleigh speed or there is a combination of these.